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Anaccurate,quickandsimplemethodtodeterminetheplasticlimitandconsistencychangesinalltypesofclayandsoil:Thethreadbendingtest.RESEARCHAUGUST2015DOI:10.13140/RG.2.1.3237.3603

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Jos-ManuelMoreno-MarotoUniversityofCastilla-LaMancha1PUBLICATION0CITATIONS

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Availablefrom:Jos-ManuelMoreno-MarotoRetrievedon:15August2015

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PlasticityBending testClay minerals

ethnt frthe

ick abjecent until they start to crack. The relationship between the bending produced, B, andstudied, in such a way that the plastic limit, PL, and another two new parameters

nsistend theundaryisolid s

meter or stressstrainmation test for metalsainly focused on theirnative method for de-

Applied Clay Science 114 (2015) 497508

Contents lists available at ScienceDirect

Applied Cla

j ourna l homepage: www.eand the friction or the speed of rolling (Whyte, 1982), as well as thesize of the sample and the type of soil. These last two factors are themain ones that affect the nal result (Temyingyong et al., 2002).

termining the plastic limit was not tackled. With the special instanceof cone penetration tests, a great deal of research has gone into deninga new methodology for PL determination without reaching any realby hand until the operator considers the soil to be crumbling (e.g. UNE103-104-93; ASTM D 431805). Therefore, the skill and judgment ofthe operator play a critical role in the outcome of the test. Many factorsare not controlled, such as the pressure applied, the contact geometry

trationmethods, capillary rheometer, torque rheocurves. Baran et al. (2001) adapted a stress-deforto study the plastic properties of clays but this mworkability, and the issue of considering an alterbased on the Casagrande method (e.g. UNE 103-103-94; ASTM D431805) or the penetration test (BS, 13772:1990). By contrast, themost popular and standardized method for PL determination, the socalled thread rolling test is based on rolling soil into 3 mm threads

(Polidori, 2003, 2007, 2009), while the underlying problem, PL determi-nation, remains unsolved.

A review of the differentmethods tomeasure soil plasticity has beenpresented by Andrade et al. (2011) including the Pfefferkorn test, pene- Corresponding author.E-mail addresses: josemanuel.moreno@uclm.es (J.M. M

jacinto.alonso@uclm.es (J. Alonso-Azcrate).

http://dx.doi.org/10.1016/j.clay.2015.06.0370169-1317/ 2015 Elsevier B.V. All rights reserved.tates, respectively.ally, dispensing with thedards around the world

this, this classication system sometimes appears unreliable, so it hasbeen the object of a great deal of criticism which has caused it to be re-vised (Gutirrez, 2006) and even to new proposals for classicationLL determination is carried out mechanicoperator judgment, according to several stan1. Introduction

Atterberg in 1911 dened seven cosoils, of which the liquid limit, LL, anmost important, since theymark the botic states, and between plastic and semence. These new parameters delimit other consistency states, whichmay be very useful in sectors such as the ce-ramics industry, agriculture or geotechnical engineering.The PL results obtained by the bending test in 24 soils concur to a great degree with those obtained in the threadrolling test by a highly experienced operator (R2 = 0.972). Moreover, these results have been endorsed by Sha-piroWilk and Student's T statistics tests. Finally, the reliability of the method using only 3 and 1 experimentalpoints has been studied too which have yielded very similar results to those obtained with 6 and 7 points.

2015 Elsevier B.V. All rights reserved.

cy limits for ne-grainedplastic limit, PL, are thebetween liquid and plas-

The international soil classication system (the Casagrande Chart)shown in ASTM D, 248700, based on the work of Casagrande (1932,1948) is a very useful tool for determining the plastic and geotechnicalproperties of soils. Errors in the PL imply that the soil has been incorrect-ly identied and classied (Sokurov et al., 2011). As a consequence ofPlastic limitSoil consistency (the stiff-soft limit, SSL, and the bend-breaking limit, BL) have been determined with minimal operator interfer-Atterberg limits ameter and 52mm long are bwater content, W, has beenAn accurate, quick and simple method to dconsistency changes in all types of clay an

Jos Manuel Moreno-Maroto, Jacinto Alonso-AzcrateUniversity of Castilla-La Mancha, Department of Physical Chemistry, Faculty of Environmental

a b s t r a c ta r t i c l e i n f o

Article history:Received 9 April 2015Received in revised form 15 June 2015Accepted 28 June 2015Available online xxxx

Keywords:

The standard thread rolling mquiring considerable judgmebeen put forward; however,time and cost.In this article an accurate, qulimit of soils, in which the suoreno-Maroto),ermine the plastic limit andoil: The thread bending test

nces and Biochemistry, Avenida Carlos III, s/n, 45071 Toledo, Spain

od for determining the plastic limit of soil, PL, has been widely criticized for re-om the operator that carries out the test. In different studies othermethods havese methods cannot compete with the thread rolling test in simplicity, execution

nd simplemethod is presentedwith a simple device for determining the plastictive point of view of the operator is omitted. Soil threads which are 3 mm in di-

y Science

l sev ie r .com/ locate /c layagreement; for example: Wroth and Wood (1978) were in favor ofobtaining the PL through the fall cone test, based on the misconceptionthat the shear strength at the PL is 100 times that at the LL; from thissame idea, Harison (1988) used a semi-logarithmicmodel to determinethe PL as the water content corresponding to a penetration value of

2 mm; by contrast, Feng (2000) applied a linear model based on a dou-ble logarithmic scale and used a ring to prepare the soil specimens (thedesign of this ring was improved in Feng (2004)); Lee and Freeman(2009) determined simultaneously the LL and PL with a dual-weightfall cone and Sivakumar et al. (2009) attached a cylinder and piston tothe usual cone apparatus in order to increase the load by air pressureand to obtain the PL at a penetration depth of 20 mm. However, all ofit is based on the assumption that the plastic limit corresponds to a de-ned shear strength, which is not correct (Haigh et al., 2013).

In othermore recentworks, such as those described by Barnes (2009,2013) the rolling conditions of soil cylinders were emulated, in whichstresses and strains and even soil workability were measured and inwhich other less well-known consistency limits could be obtained. Inprinciple, theBarnesmethod appears towork, although some shortcom-ings have been identiedwith this approach:many experimental pointsand extensive data processing are required (which increases complexityand test time). Furthermore, a relatively complex apparatus is necessary(which increases cost and complexity). Additionally, themain issue, thatis, themeans of obtaining the PL is questionable, since this is done by anarithmetic mean between two points (one on each side of the PL) andstrictly speaking, the PL does not have to be the average in that range,but could be anymoisture value included in it. Therefore, so as to curtailthe importance of this, the Barnes method requires the moisture valueson either side of the PL to be very similarwhich undoubtedlywould lead

samples presented different grain-sizes and compositional characteris-tics (Table 1), so a good representativeness of different types of soilwas obtained. All samples were stored in polyethylene bags and thenthey were reduced by quartering to keep the original representative-ness and homogeneity.

The soil was dried in an oven at a temperature of 55 C. Subsequent-ly, it was disaggregatedmanually by amortar and rubber covered pestleand passed through a 0.40 mm sieve. Fractions of under 0.40 mm wereused in the tests.

2.2. Mineralogical study, particle size distribution and Atterberg limits bystandard methods

The mineralogical study of the soil samples was carried out bymeans of X-ray diffraction (XRD) analysis. The clay mineralogy was de-termined in oriented aggregates (OA) of the b2 mm fraction obtainedby sedimentation from an aqueous suspension onto glass slides andwere examined on a PANalytical diffractometer, X'Pert Pro model.The conditions used were: 45 Kv, 40 mA, CuK radiation and a systemof slits (sollermaskdivergenceantiscatter) of 0.04 rad10 mm1/81/4 with an X'celerator detector. The OAwere subjected to thermaltreatment at 550 C for 2 h and to solvationwith ethylene glycol at 60 Cfor 48 h.

L: m

osededintaay a

th p

ray

y 200220 cm Ill, Kao, Chl, MLbenwnnta

(bu

l gr

498 J.M. Moreno-Maroto, J. Alonso-Azcrate / Applied Clay Science 114 (2015) 497508to an increase in the time and difculty of the test.Apart from the inherent weaknesses of the methods described

above, not all of them are viewed as being possible alternatives to thethread rolling test, since they cannot compete against it in terms of sim-plicity, execution time and cost. This must be why the thread rollingmethod continues to be themostwidely used test for PL determination.

In this article, a new and simple method is presented. The threadbending test (or simply bending test) allows not only the PL, but alsoother parameters related to soil consistency to be obtained accurately,so a real and practical alternative is offered to the traditional method.

2. Materials and methods

2.1. Sampling and initial preparation of test samples

Twenty four soil samples were collected from different geologicallocations throughout the province of Toledo (central Spain). This way

Table 1Soil sources and general description. Sm: smectite, Ill: illite, Kao: kaolinite, Chl: chlorite, M

Soil name Location or source General description

M1 Valdehierro Valley Madridejos Brownish-gray descompM2 Valdehierro Valley Madridejos Dark-brown sandy silt (sM3 Valdehierro Valley Madridejos Dark-brown silt (sedimeM4 Urda area private company Commercial brownish grM5 La Sagra area Pantoja Brown clayM6 Valdehierro Valley Madridejos Mustard-colored clay wiM7 Madridejos agricultural soil Red clayM8 La Sagra area Borox Highly calcareous light-gM9 La Sagra area Borox Greenish sandy clayM10 Tembleque agricultural soil Calcareous brown clayM11 La Sagra area Pantoja Brown sandy soilM12 La Sagra area Pantoja Highly plastic brown claM13 La Sagra area private company Commercial light-brownM14 Southwestern Toledo Highly descomposed broM15 Valdehierro Valley Madridejos Dark-brown silt (sedimeM16 Madridejos agricultural soil Brown silty clayM17 Valdehierro Valley Madridejos Red clayM18 Madridejos agricultural soil Orange clayM19 Valdehierro Valley Madridejos Brown siltM20 Madridejos city Brown silt with gypsumM21 Villarrubia de Santiago Calcareous beige siltM22 Mixture 15% M12 + 85% M16M23 Mixture 15% M13 + 85% M16M24 Almonacid de Toledo area private company Commercial gray articiatonite 050 cm (material pile) Sm, Ill, Kaoish granite 2040 cm Ill, Sm, Kaory deposits on a stream bank) 020 cm Ill, Chl, Kao

220 cm Ill, Kao, ML3040 cm Sm, Kao, Ill, ML220 cm Ill, Kao, ML2030 cm Ill, Kao, ML

ilding waste) 030 cm Ill, Kao, Sm, ML2040 cm Ill, Kao, MLSee M12 and M16 Ill, Kao, MLSee M13 and M16 Sm, Ill, Kao

aded aggregate 050 cm (material pile) Sm, Ill, KaoParticle size distribution of soils was determined according to ASTMD 42263 (1998). Fractions above 63 m were determined by sievingand the silt-clay fraction by sedimentation with a 152H (ASTM E10005) Bouyoucos hydrometer. From the grain size distribution data,soils were classied according to the internationally accepted Soil Tex-ture Triangle (USDA, 1993).

For determining the Atterberg limits, soils were previously amassedwith distilled water. The amount of added water was that necessary toprovide a soil consistency that would require about 25 to 35 blows inthe LL test, aswell as that atwhich the soil can be rolledwithout stickingto the hands for the PL test. Each homogeneous soilwater mixturewas stored for 24 h under hermetic conditions in polyethylene bags,thereby, preserving their initial moisture content. The liquid limit, LL,and plastic limit, PL, were determined by the Casagrande method andthe thread rolling test in accordance with the UNE 103-103-94 andUNE 103-104-93 standards, respectively and homologous to the ASTMD 431805 standard.

ixed layer clay minerals.

Sampling depth Clay mineralogy

granite (articially material pile) 050 cm (material pile) Sm, Ill, Kaomentary deposits on a stream bank) 020 cm Ill, Kaory deposits on a stream bank) 2030 cm Ill, Kaorticial graded aggregate 050 cm (material pile) Sm, Ill, Chl, Kao, ML

120140 cm Ill, Kao, Smebbles and gravel 3040 cm Ill, Kao, Sm, ML

220 cm Ill, Kao, MLsilty clay 100120 cm Sm, Ill

100120 cm Sm, Ill, Kao, ML220 cm Ill, Kao, Chl, Sm, ML140160 cm Ill, Kao, Chl, Sm, ML

Both methods were carried out by a highly experienced operator(with a record of having carried out over 4000 plasticity tests) to ensurethat the tests were properly carried out and thus to compare sound PLthread rolling results with those obtained by the method proposed inthis study.

2.3. The thread bending test

Just as with the LL and PL standard test, soils were homogeneouslyamassed with distilled water. In this case, 3 to 5 different soil moistureballs were prepared. Each soilwater ball of 3040 g approx. was storedfor 24 h under hermetic conditions in polyethylene bags.

After this tempering period, each ball of soil was tested as follows:The soil ballwasattened on a nonabsorbent smooth glass plate. The

atteningwas performed by hand (preferably using latex gloves to pre-vent loss of soil moisture) until the thickness was slightly higher than3 mm; at this point, an aluminum tool designed in this research calledthe threadmolder (Fig. 1a, b, c and Fig. 2) was used to obtain a thicknessof exactly 3 mm (the thread molder is described in more detailedbelow).

The jagged edges of the soil mass were cut with a metal spatulaafter which a strip that was at least 52 mm long and a square sectionof approximately 3 3mmwas cut. From this strip, a cylindrical threadwith a diameter of exactly 3mmwhich was 52mm longwas shaped bythe threadmolder: the threadmolder (Fig. 1a) is designed in such awaythat there is a space of exactly 3mmbetween the partwhich shapes the

soil thread and the glass plate. The thread molder was successivelymoved backwards and forwards by hand until the exact moment atwhich the initially square section of the soil thread became round(Fig. 2a). The 3 mm round section thread was cut with a metal spatulafor which the width of the thread molder was employed as a template(it measures 52 mmwide) in order for it to measure 52 mm in length.Then, on the same glass plate, the soil thread was bent according toFig. 2b and Fig. 3a, b. To do so, the steel pushers designed (Fig. 1d, eand Fig. 2b) were used as mobile supporting points and a cylindricalpart of the thread molder worked as a xed supporting point. Bendingwas stopped at the point of cracking. Right afterwards, the distancebetween the tips of the thread was measured with a caliper and record-ed to a precision of 0.1 mm. This measurement was taken from thecentral part of the tips (Fig. 3c). When the soil is very wet, deectionscan be so large that even the thread tips come into contact (Fig. 3d).In this case, the soil thread was bent by hand (the pushers and threadmolderwere not necessary) until the point of cracking as is shown sche-matically in Fig. 3e. The distance between the thread tips was taken asshown in Fig. 3f and Fig. 4, but here the value was recorded with a neg-ative sign.

All these steps were repeated for at least two other soil threads. Al-ternatively other cylinders were shaped exactly like those that werebent, but their tips were not cut since they were simply used to obtainenough material to correctly determine their moisture content (a min-imum of 5 g is recommended). The material was put into a containerwhose weight was known and was weighed to a precision of 0.01 g. It

view

499J.M. Moreno-Maroto, J. Alonso-Azcrate / Applied Clay Science 114 (2015) 497508Fig. 1.Drawings and dimensions inmmof the threadmolder and the steel pushers. (a) Side

the steel pushers., (b) top viewand (c) bottomviewof the threadmolder; (d) front viewand (e) top viewof

was dried in an oven for a minimum of 24 h at 105 C until its weightwas constant in order to determine its moisture content (W).

the Atterberg limits (Schmitz et al., 2004). For example, typical A valuesare: 1.25 to 7 for smectite (active clays), 0.75 to 1.25 for illite (normal

)

Fig. 2. (a) Shaping of a soil thread with the thread molder and size of the soil strip to be cut. (b) Bending of a soil thread; the arrows indicate the bending technique.

500 J.M. Moreno-Maroto, J. Alonso-Azcrate / Applied Clay Science 114 (2015) 497508This whole process was repeated with the other soil balls that hadbeen prepared earlier. Different moisture contents were also obtainedby mixing balls or by hand drying, so between 3 and 7 experimentalpoints were obtained.

3. Results and discussion

3.1. Mineralogical study, particle size distribution and Atterberg limitsaccording to standardized methods

As can be seen in Table 2, there are a wide range of soils in terms ofplastic and particle-size properties. According to the USDA textureclassication (1993) there are sandy, silty, clayey and intermediate-grained soils in this study. Likewise, the Atterberg limits results andCasagrande classication show soils with very low (M4 and M21), low(M2, M6, M11, M14, M15, M16, M19 and M24), medium (M1, M3,M7, M10, M17, M18, M20 and M22), medium-high (M5 and M23),high (M8, M9 and M12) and very high plasticity (M13). Anotherproperty that is also shown is the so called activity, A, introduced bySkempton in 1953 as the ratio of plasticity index (PI = LLPL) tob2 m clay fraction. Despite the fact that the Skempton activity indexis unable to show accurate mineralogical results, it is a sound indicator,in general terms, of the type of clay contained in soil which inuences

(a) (b(d) (e)

Fig. 3. Schematic drawingwhere bending and tip distancemeasurement techniques are detaileda cracked thread. (d) Soil thread inwhich tips come into contact and can form a closed ring. (e)and (f) the measurement technique for this last case.clays) and less than 0.75 for kaolinite (inactive clays). In this regard, awide variety of Skempton activity data can be observed: active soils(M8, M13), normal soils (M9, M23) and inactive soils (the remainingsamples), which shows that the tested soils have different chemicaland mineralogical compositions. This last aspect is ratied in Table 1,where it is observed a wide representativeness of clay minerals, witha signicant presence of smectite, illite, kaolinite, chlorite and mixed-layer clay minerals, which vary depending on the soil sample.

Taking into account the wide heterogeneity of the samples, in prin-ciple, the results and conclusions of this research could be applied toany type of soil, whatever its properties are.

3.2. Initial data processing

Anewparameter called bending at cracking or simply bending, B, wasdevised to ascertain the extent of bending that the cylindrical soilthreads were subject to for each moisture content:

B 52:0D 1

where, D is the average distance measured between the tips at the timeof cracking and 52.0 refers to the length in mm of the soil thread.

(c) (f)

D

cracking

cracking

. (a) Initial position. (b) Usual bending technique and (c) usualmeasurement technique ofBending technique to be followedwhen the soil thread is able to bend beyond a closed ring

Bending values, B, obtained from Eq. (1) were plotted against watercontent, W. Between 3 and 7 BW experimental points were obtainedfor each soil (Fig. 5). In all cases, the correlation of the points can bedened in two ways, without compromising in any way the correctdenition of the point path: as a parabolic curve (Fig. 6a) or as twointersecting lines (Fig. 6b).

The parabolic curve was named the bending curve (Fig. 6a) whoseequation is:

W z Bm 2

has been observed in the water contents corresponding to the steepestline, whereas the consistency state in the less steep line was viewed asbeing soft-plastic. As water works as a lubricant between the claysheets, the stiffer the soil, the more water will be needed to deform it(here deformation is by bending). This makes sense, since a steeperslope indicates that more water is required to bend the thread soil be-cause of its stiffness, while a gentler slope indicates that the soil threaddoes not need a lot of water to bend easily, since this is in a softer state.In fact, the shape of the graphs obtained by the thread bending test, likethe one shown in Fig. 6b, are very similar to others obtained by muchmore complex stressstrain tests, e.g. those obtained by Barnes (2009,2013) and even the same consistency states have been perceived.

Therefore, the steepest line corresponds to lower B values andmois-ture contents in which the soil has a stiff-plastic consistency, hence itsname, the stiff-plastic line which is dened by the following equation:

W jstiff B cstiff 3

where, jstiff is the value of the stiff-plastic line slope and cstiff is a con-stant that corresponds to the cutoff point of the stiff-plastic line withthe y-axis.

Conversely, the gentler line denes the range of moisture in whichthe soil is soft-plastic andworkable, without actually being really sticky.This second line is called the soft-plastic line and is dened as:

dissho

cracking

Fig. 4. Tip distancemeasurement of a veryexible threadwith a caliper just after cracking.

501J.M. Moreno-Maroto, J. Alonso-Azcrate / Applied Clay Science 114 (2015) 497508where z is a constant,m is the so called bending slope that is the value ofthe straight line slope formedwhen the bending curve is represented indouble logarithmic scale. All other terms were dened previously.

As noted above, the arrangement of the points may also be denedby two straight lines with different slopes which intersect at an inter-mediate point (Fig. 6b). This cutoff point corresponds to amoisture con-tent at which a change of consistency occurs. Despite the fact that thethread bending test does notmeasure stresses, a stiff-plastic consistency

Table 2Percentages of clay, silt and sand and USDA texture classication according to the grain sizedards and Casagrande plasticity classication. Skempton activity (A) of each soil sample is

Soil % clay(b2 m)

% silt(263 m)

% sand(N63 m)

USDA textureclassication

M1 19.92 18.60 61.48 Sandy loamM2 16.49 36.24 47.27 LoamM3 18.03 62.89 19.08 Silt loam

M4 12.39 49.03 38.58 LoamM5 57.29 26.64 16.07 ClayM6 33.05 27.86 39.09 Clay loamM7 44.88 30.76 24.37 ClayM8 18.50 68.45 13.05 Silt loamM9 25.63 27.32 47.05 Sandy clay loamM10 33.57 49.38 17.05 Silty clay loamM11 20.58 10.37 69.05 Sandy clay loamM12 66.47 31.16 2.38 ClayM13 67.79 26.06 6.15 ClayM14 19.44 16.43 64.12 Sandy loamM15 14.31 51.45 34.23 Silt loamM16 31.01 46.38 22.61 Clay loamM17 36.87 46.23 16.89 Silty clay loamM18 41.89 26.38 31.73 ClayM19 19.48 52.79 27.72 Silt loamM20 20.88 48.71 30.41 LoamM21 13.30 48.34 38.36 LoamM22 35.37 44.56 20.07 Clay loamM23 34.77 45.00 20.24 Clay loamM24 20.97 28.98 50.05 Loam

a Classication system shown in the standard ASTM D 248700.W jsoft B csoft 4

where, jsosft is the value of the soft-plastic line slope and csoft is a con-stant that corresponds to the cutoff point of the soft-plastic line withthe y-axis.

Being able to describe the point path both as a parabolic curve and astwo straight lines is, as will be seen later, a very useful tool to denechanges in soil consistency, without obtaining a large number of exper-imental points.

tribution. Results of LL, PL and PI according to UNE 103-103-94 and UNE 103-104-93 stan-wn in the last column.

LL PL PI(LLPL)

Casagrandeclassicationa

Activity(PI/% b 2 m)

33.8 19.3 14.5 CL 0.7326.9 18.8 8.1 CL 0.4931.8 21.0 10.8 CL 0.6016.3 12.5 3.8 ML 0.3149.4 21.0 28.4 CL/CH 0.5028.0 13.2 14.8 CL 0.4535.1 14.6 20.5 CL 0.4683.3 30.1 53.2 CH 2.8880.0 49.7 30.3 MH 1.1834.9 20.0 14.9 CL 0.4422.8 12.9 9.9 CL 0.4862.5 28.1 34.4 CH 0.52

214.4 37.1 177.3 CH 2.6229.5 20.0 9.5 CL 0.4921.9 16.2 5.7 CLML 0.4026.2 16.0 10.2 CL 0.3336.9 17.1 19.8 CL 0.5430.3 14.9 15.4 CL 0.3722.0 13.7 8.3 CL 0.4333.1 17.9 15.2 CL 0.7314.3 13.7 0.6 ML 0.0531.6 16.0 15.6 CL 0.4448.7 17.0 31.7 CL 0.9126.2 15.6 10.6 CL 0.51

e tested

502 J.M. Moreno-Maroto, J. Alonso-Azcrate / Applied Clay Science 114 (2015) 4975083.3. Parameters obtained from the thread bending test

Considering the above, the stiff-plastic and soft-plastic lines are use-ful tools to establish the limits between different consistency statesfrom the following parameters:

Plastic limit, PL: Strictly speaking, the plastic limit corresponds to amoisture content at which the soil is no longer able to resist defor-mation, and so it breaks immediately when attempts are made todeform it. The PL for the bending test is based on this and is obtainedas themoisture content that corresponds to a bending of B= 0mm,so that, the soil is not capable of withstanding deformations belowthis threshold (nonplastic state) but it does bear themabove it (plas-tic state). Therefore, the PL is the moisture percentage correspond-ing to the cutoff point of the stiff-plastic line with the y-axis, that is:

PL cstiff 5

Bend-breaking limit, BL: This is a new parameter obtained from thesoft-plastic line as the moisture content, W, corresponding to B =88.4 mm. This is the threshold value above which the soil thread issoft enough to bend completely without breaking. Thus, the soilsmostly have a quite soft and sticky consistency when their moisturecontents are close to the BL.

Fig. 5. (a) Experimental points obtained from the thread bending test for all thBL jsoft 88:4 csoft 6

Fig. 6. Graphical representation of the BWpoints for the soil M22 drawn as (a) a parabolic curve osoft-plastic line (b) are included.B value = 88.4 was obtained according to Fig. 7. It was consideredthat the cylindrical soil thread forms a circumference with radius,r, equal to 3 mm in the bending area.In this way, DBL and BBL were obtained as follows:

DBL 52:0 3=4 circumference perimeter r=2 7

where DBL is the distance between the thread tips for the BL mois-ture content, whose result is DBL =36.36 mm and r is the radiusequal to 3 mm.Thus, according to Eq. (1): BBL = 52(36.36) = 88.36 mmi.e., BBL = 88.4 mmwhere BBL is the bending at cracking for a mois-ture content equal to BL (in this case cracking does not occur).Because of the difculty of handling a 3 mm soil thread at or abovethe BLwater content (the consistency is sticky or too soft), the resultof D = 36.36 (i.e., B = 88.4 mm) was experimentally veriedusing plasticine. The result obtained was the same as that calculatedfrom Eq. (6) and Eq. (7).Stiff-soft limit, SSL: The SSL is a new parameter dened as the mois-ture percentage corresponding to the intersection point of the stiff-plastic line with the soft-plastic line. SSL marks the transition pointbetween stiff-plastic and soft-plastic consistency states and is deter-mined from the stiff-plastic line equation or the soft-plastic line

soils. (b) More detailed view for samples with water contents below 35%.equation as:

SSL j BSS c 8

r (b) as two intersecting lines. Equations of the bending curve (a), stiff-plastic line and

where j is jstiff or jsoft, c is cstiff or csoft and BSS is the bending at crack-ing, B, for the SSL moisture, which is obtained as:

BSS csoft cstiff = jstiff jsoft 9

Apart from the typical liquid, plastic and semisolid (or brittle) statesdened by the LL and PL, the new parameters, SSL and BL, allow otherconsistency states in clays and cohesive soils within the plastic regionto be delimited, such as stiff-plastic (between PL and SSL), soft-plastic(between SSL and BL) or very soft-sticky (between BL and LL) (Fig. 8a,b). However BL and SSL usually appear positioned above the LL in verylow plasticity soils (Fig. 8a, d, f), and the consistency in this case be-tween the LL and BL or SSL may be dened as liquid but not entirelydeformable (the ability to be completely deformed is acquired whenwater contents are above BL). Similarly, it may occur that LL = BL orLL= SSL (Fig. 8a, c, e), so that in the former, the consistency changes di-rectly from soft-plastic to liquid, and in the latter, from stiff-plastic toliquid which is not entirely deformable. Therefore, BL and SSL could

(a)

(b)

(c)

(d)

(e)

(f)

(g)

Soft-Plastic

PL LLSSL Moisture contentBL

Liquid but not enterely

deformableStiff-PlasticSemisolid Liquid

PL SSL=LL

Stiff-PlasticSemisolid Liquid but no

PL LL

Stiff-PlasticSemisolid Liquid but no

PLLL SSL

Liquid but not enterely deformable (No plastic state)Semisolid

Very soft-Sticky

PL BLSSL Moisture contentLL

Soft-PlasticStiff-PlasticSemisolid Liquid

Liquid

PL BL=LLSSL Moisture content

Soft-PlasticStiff-PlasticSemisolid

LLLLLLLLLL

ExtremelyLow

plasticityLL

PL BLSSL

Very High plasticity

LL

Moisture content

Practically Non-plastic

High plasticity

Lowplasticity

Very Low

plasticityMedium plasticityNon-plastic

LL

Fig. 8. (a) Schematic classication of soil plasticity depending on the LL value with regarplasticity, (c) low plasticity, (d) very low plasticity, (e) extremely low plasticity, (f) practicalin (bg).

Fig. 7. Schematic representation of a fully bent 3mmdiameter 52mm length soil thread.The necessary dimensions to calculate the distance between the thread tips (D) are indi-cated (drawing is not to scale).

503J.M. Moreno-Maroto, J. Alonso-Azcrate / Applied Clay Science 114 (2015) 497508BL Moisture content

Liquidt enterely deformable

SSL MoisturecontentBL

Liquidt enterely deformable

BL Moisture content

Liquid (No plastic state)

d to BL, SSL and PL. Consistency states identied in (b) medium, high and very highly non-plastic and (g) non-plastic soils. LL position is bordered to be more easily located

have great potential in geotechnical engineering, agriculture or aboveall in the ceramics industry, where the material consistency must beperfectly controlled in the LLPL range to optimize production andobtain awless products. With special regard to SSL, the moisture per-centage marked by this parameter could be used as the optimumwater content for molding ceramic clays, since below the SSL, the claymay crack more easily because of its stiffness, whereas above the SSLit could lose shape or stick to the work surfaces as it would be too soft.A schematic graph of the results and stiff-plastic and soft-plastic linesobtained in the soilM5 is represented (Fig. 9), since this clay has optimalplastic characteristics for ceramics (Marsigli and Dondi, 1997). SSL isrepresented as the optimumwater content for molding this clay in a ce-ramic process because higher or lower water contents could affect neg-atively to the extrusion and molding process as indicated above.

Since neither the PL nor the SSL can be calculated from the bendingcurve (neither B= 0 values can be obtained from this nor can a specictransition point be readily recognized in the curve), a priorimanypointsare required in order to successfully calculate the PL, BL and SSL from

were those corresponding to B = 5, 7.5, 10, 15, 25, 35, 45, 55, 65 and

sults were normally distributed, since the p-values were greater than0.05 i.e. the null-hypothesis was accepted (the data had a normal distri-bution). Therefore a Student's T test could be applied.

As the p-values in the Student's T test were greater than the 0.05alpha-level (Table 4), null-hypothesis was accepted, i.e. there were nosignicant differences between the PL results determined with bothmethods. Therefore, the thread bending test was very accurate, sinceits results were largely consistent with those obtained by a highly expe-rienced operator. Nevertheless, it is highly likely that if the threadrolling test had been carried out by another operator, for example, onelacking in experience or skill, signicant differences would have almostcertainly been recorded. In fact, even for a highly experienced operator,the subjective judgment needed to appreciate the crumbling conditioncan change for soils with different characteristics. For the above reasonsit can be reafrmed that the new thread bending test is a more reliablemethod, with respect to the standard thread rolling test, for determin-ing the plastic limit, since the bending test is accurate, free of subjectivejudgments and can be carried out with guarantees even by an inexperi-

504 J.M. Moreno-Maroto, J. Alonso-Azcrate / Applied Clay Science 114 (2015) 49750875mm, which were well distributed along the entire x-axis. In particu-lar instances one more point below B = 5 mm was added, but this isonly recommendable when the stiff-plastic line has not been clearly de-ned with the other points. Even so, the value of this additional pointshould never be under the lowest of those experimentally obtained.The experimental points plus the extra ones were plotted, from whichthe stiff-plastic and soft-plastic lines were drawn and whose equationswere obtained to determine PL, BL and SSL, as shown in Fig. 10 for thesoil M22.

3.4. The plastic limit by the thread bending test and the new parameters

The results obtained for the 24 soil samples are shown in Table 3. Ascan be seen, the bending curve, stiff-plastic and soft-plastic line equa-tions exhibited highly acceptable correlations, with high R2 coefcients,so equations and data calculated from them were highly reliable.

Data shows that the PL results from the new thread bending testwere quite similar to those obtained by a highly experienced operator

Fig. 9. Schematic graph of the results and stiff-plastic and soft-plastic lines obtained in thesoil M5. SSL is represented as the optimumwater content formolding this clay in a ceram-the straight lines, which entail increasing the test time. However, al-though the bending curve cannot be used for calculating the parametersit can be drawn properly with just a few points (in principle only 3points would be required (this will be covered in Section 3.5)). Consid-ering that the bending curve and the stiff-plasticsoft-plastic lines fol-low very similar paths, the bending curve equation obtained from theexperimental data (Eq. (2)) has been used to obtain extra points to,rstly, correct any deviation, and, secondly, to carry out the test withjust a fewpoints. In order to unify the criteria the extra points calculatedic process.using the standard test. In general the results obtained were slightlylower than those yielded from the thread rolling test. In 14 of the 24samples tested, the results from the new bending test were somewhatlower than those obtained with the standard method whose resultswere higher in 9 soils and coincided in one (M11). Nevertheless, the dif-ferences perceived were quite narrow: the average of the differencePLbendingPLrolling was only0.4 percentage points with a standard de-viation of 1.7, which in absolute value terms worked out at a differenceof 1.3 percentage points with a standard deviation of 1.1. These differ-ences always lied between a maximum and minimum value of 3.2 and3.8 percentage points which corresponded to the samples M9 andM12 respectively.

This is more clearly demonstrated in Fig. 11, where the line formedbetween the PL results among the two tests is very close to the 1:1line and where an excellent alignment of points can be observed(R2= 0.972). The PL-line and 1:1 line intersect at the point correspond-ing to PL=23.9, so below this the general trendwas for lower PL resultsto be obtainedwith the bending test than those from the rolling test andthe opposite was true above the intersection point. Even so, the differ-ences in the results yielded were very low.

To verify that there were no signicant differences among theresults, a Student's T test was applied after checking the data was nor-mally distributed with a ShapiroWilk test using the software SPSS Sta-tistics. As the soils were very heterogeneous, two different populationswere differentiated: high plastic soils (soils M8, M9, M12 and M13),and medium and low plasticity soils (the rest of the soils). There wasconsidered to be a condence interval of 95%, i.e. with an alpha-levelof 0.05. The ShapiroWilk test (Table 4) demonstrated that all the PL re-

Fig. 10.Graphical representation of the experimental points togetherwith the extra pointsfor the soil M22 and the resulting stiff-plastic and soft-plastic lines and their equations.enced operator.

Table 3Results obtained by the thread bending test.

Soil Bending curvea Stiff-plastic linea Soft-plastic linea PLbending PLbendingPLrolling PIbending Casagrandeclass

BL SSL BSS LLBL LLSSL Exp.points

Extrapointsb

Totalpoints

M1 y = 18.375(x^0.113)R2 = 0.954

y = 0.476x + 19.101R2 = 0.873

y = 0.092x + 23.914R2 = 0.891

19.1 0.2 14.7 CL 32.0 25.1 12.5 1.8 8.7 7 10 17

M2 y = 13.900(x^0.139)R2 = 0.949

y = 0.315x + 15.911R2 = 0.871

y = 0.083x + 19.540R2 = 0.972

15.9 2.9 11.0 CL 26.9 20.8 15.6 0.0 6.1 6 10 16

M3 y = 18.136(x^0.097)R2 = 0.938

y = 0.273x + 19.651R2 = 0.939

y = 0.064x + 23.137R2 = 0.884

19.7 1.3 12.1 CL 28.8 24.2 16.7 3.0 7.6 4 10 14

M4 y = 10.772(x^0.129)R2 = 0.988

y = 0.199x + 12.392R2 = 0.980

y = 0.052x + 15.108R2 = 0.961

12.4 0.1 3.9 ML 19.7 16.1 18.5 3.4 0.2 5 10 15

M5 y = 20.985(x^0.061)R2 = 0.962

y = 0.263x + 21.761R2 = 0.774

y = 0.039x + 24.530R2 = 0.950

21.8 0.8 27.6 CL/CH 28.0 25.0 12.4 21.4 24.4 4 10 14

M6 y = 14.125(x^0.093)R2 = 0.962

y = 0.478x + 13.626R2 = 0.912

y = 0.051x + 17.559R2 = 0.882

13.6 0.4 14.4 CL 22.1 18.0 9.2 5.9 10.0 5 11c 16

M7 y = 14.846(x^0.124)R2 = 0.972

y = 0.564x + 14.937R2 = 0.883

y = 0.076x + 20.046R2 = 0.965

14.9 0.3 20.2 CL 26.8 20.8 10.5 8.3 14.3 5 10 15

M8 y = 33.759(x^0.193)R2 = 0.996

y = 2.489x + 32.788R2 = 0.945

y = 0.380x + 51.449R2 = 0.965

32.8 2.7 50.5 CH 85.0 54.8 8.8 1.7 28.5 6 11c 17

M9 y = 54.097(x^0.072)R2 = 0.991

y = 1.713x + 52.890R2 = 0.931

y = 0.169x + 62.556R2 = 0.937

52.9 3.2 27.1 MH 77.5 63.6 6.3 2.5 16.4 5 10 15

M10 y = 20.851(x^0.057)R2 = 0.965

y = 0.309x + 20.929R2 = 0.949

y = 0.040x + 23.903R2 = 0.965

20.9 0.9 14.0 CL 27.4 24.3 11.1 7.5 10.6 5 10 15

M11 y = 11.279(x^0.133)R2 = 0.989

y = 0.233x + 12.874R2 = 0.925

y = 0.054x + 16.162R2 = 0.982

12.9 0.0 9.9 CL 20.9 17.2 18.4 1.9 5.6 3 10 13

M12 y = 22.481(x^0.130)R2 = 0.997

y = 0.622x + 24.344R2 = 0.982

y = 0.122x + 30.864R2 = 0.972

24.3 3.8 38.2 CH 41.6 32.5 13.0 20.9 30.0 5 10 15

M13 y = 33.906(x^0.072)R2 = 0.985

y = 0.360x + 36.218R2 = 0.971

y = 0.080x + 40.621R2 = 0.966

36.2 0.9 178.2 CH 47.7 41.9 15.7 166.7 172.5 4 10 14

M14 y = 14.990(x^0.129)R2 = 0.972

y = 0.247x + 17.490R2 = 0.942

y = 0.071x + 21.216R2 = 0.939

17.5 2.5 12.0 CL 27.5 22.7 21.2 2.0 6.8 7 10 17

M15 y = 13.337(x^0.101)R2 = 0.979

y = 0.170x + 14.976R2 = 0.984

y = 0.044x + 17.470R2 = 0.984

15.0 1.2 6.9 CLML 21.4 18.3 19.8 0.5 3.6 3 10 13

M16 y = 13.952(x^0.101)R2 = 0.982

y = 0.200x + 15.442R2 = 0.969

y = 0.045x + 18.326R2 = 0.980

15.4 0.6 10.8 CL 22.3 19.2 18.6 3.9 7.0 4 10 14

M17 y = 14.727(x^0.099)R2 = 0.984

y = 0.147x + 16.799R2 = 0.930

y = 0.047x + 19.237R2 = 0.980

16.8 0.3 20.1 CL 23.4 20.4 24.4 13.5 16.5 3 10 13

M18 y = 15.448(x^0.079)R2 = 0.989

y = 0.357x + 15.619R2 = 0.968

y = 0.050x + 18.357R2 = 0.954

15.6 0.7 14.7 CL 22.8 18.8 8.9 7.5 11.5 5 10 15

M19 y = 9.932(x^0.145)R2 = 0.851

y = 0.232x + 11.568R2 = 0.872

y = 0.070x + 13.853R2 = 0.955

11.6 2.1 10.4 CL 20.0 14.8 14.1 2.0 7.2 6 10 16

M20 y = 17.617(x^0.085)R2 = 0.868

y = 0.175x + 19.171R2 = 0.799

y = 0.037x + 22.702R2 = 0.703

19.2 1.3 13.9 CL 26.0 23.6 25.6 7.1 9.5 6 10 16

M21 y = 9.901(x^0.140)R2 = 0.869

y = 0.202x + 11.525R2 = 0.979

y = 0.056x + 14.177R2 = 0.953

11.5 2.2 2.8 ML 19.1 15.2 18.2 4.8 0.9 5 10 15

M22 y = 15.020(x^0.087)R2 = 0.934

y = 0.251x + 15.880R2 = 0.860

y = 0.050x + 18.475R2 = 0.930

15.9 0.1 15.7 CL 22.9 19.1 12.9 8.7 12.5 6 10 16

M23 y = 16.111(x^0.095)R2 = 0.934

y = 0.251x + 17.437R2 = 0.974

y = 0.067x + 19.889R2 = 0.921

17.4 0.4 31.3 CL 25.8 20.8 13.3 22.9 27.9 6 10 16

M24 y = 13.343(x^0.120)R2 = 0.997

y = 0.340x + 14.310R2 = 0.979

y = 0.062x + 18.048R2 = 0.952

14.3 1.3 11.9 CL 23.5 18.9 13.4 2.7 7.3 4 10 14

av. md 0.108 av. 0.4 av. 15.0sd md 0.032 sd 1.7 sd 4.9av. me 0.108 max 3.2 max 25.6sd me 0.033 min 3.8 min 6.3

a y =W and x = B in the equations.b Number of extra points included in the analysis. Extra points are those calculated for B = 5, 7.5, 10, 15, 25, 35, 45, 55, 65 and 75 mm.c Other than indicated on b, an additional extra point was added: B = 2 mm in M6 and B = 3 mm in M8.d Average and standard deviation of the bending slopes, m, that appear in bold in each bending curve equatione Average and standard deviation of the bending slopes, m, that appear in bold in each bending curve equation but 3-point soils (M11, M15 and M17) are not included. 505

J.M.M

oreno-Maroto,J.A

lonso-Azcrate/A

ppliedClay

Science114

(2015)497508

506 J.M. Moreno-Maroto, J. Alonso-Azcrate / Applied Clay Science 114 (2015) 497508The Plasticity index, PI, is directly related to the PL value (PI = LLPL), so the same variations observed in the PL have been perceived inthe PI (Table 3). As the PL differences between the methods are quitesmall, the PI results have not changed signicantly and thus, no changein the Casagrande classication has been registered.

Concerning the newparameters (which are the bend-breaking limit,BL, and the stiff-soft limit, SSL, in Table 3) awide variety of results can beseen, most of which show values around 20 to 30, although in moreplastic soils, M8, M9, M12 and M13, greater BL and SSL values were ex-hibited. The LL position regarding BL and SSL (LLBL and LLSSL col-umns) revealed LL to be greater than BL in most cases. NeverthelessBLwas higher than LL in soilsM4,M8 andM21,which indicated that be-tween the LL and the BL there was a consistency state that despite beingliquid, was not entirely deformable. For the soil M21, SSL was higherthan LL, because this was essentially a nonplastic soil. The M8 soil hadunusual properties, since although LL and PI values were high, therewas poor resistance to bending. A DRX analysis with a Philips X'PertMPD X-ray diffractometer revealed that in the M8 soil there was agreat deal of calcite combined with smectite which was the main clay

Fig. 11. Plastic limit results from the new thread bending test against those from the tra-ditional thread rolling test.component. The smectite could explain why there was high LL and PI,since smectite minerals are related with very high Atterberg limits re-sults (White, 1949), whereas the calcite could explain the low bendingcapacity because this acts as a cement that affects the soil properties andreduces the plasticity (Datta et al., 1982). In theM2 soil, LL = BL, so theconsistency changed directly from soft-plastic to liquid, and there wasno detection of any consistency that was very soft or sticky within theplastic state. Furthermore, the BSS results indicate that the stiff-softlimit is normally located at an average of B = 15 mm, but this value

Table 4Test of normality of ShapiroWilk for PL results of high and low-medium plasticity soilsaccording to bending and rolling tests. In bold, test of Student's T for the results of PL ob-tained by the thread bending test against the thread rolling test; high and low-mediumplasticity soils are differentiated.

Variable Statistic df p-Value

ShapiroWilk test for PL bending high plasticity 0.947 4 0.700ShapiroWilk test for PL rolling high plasticity 0.897 4 0.414ShapiroWilk test for PL bending low-medium plasticity 0.968 20 0.708ShapiroWilk test for PL rolling low-medium plasticity 0.943 20 0.276Student's T test (bilateral) for PL of high plasticity soils 0.183 3 0.867Student's T test (bilateral) for PL of low-mediumplasticity soils

1.833 19 0.083changes at intervals between 6.3 (M9) and 25.6 (M20). All these newparameters, therefore, show other features that may be of interest andthat LL and PL cannot obtain by themselves.

3.5. Feasibility of the method using only 3 points and the importance of thebending slope, m

The soilsM11,M15 andM17were testedwith only 3 points. In orderto verify if the results obtained from these three samples were correctand if a 3-point test would be reliable, a statistical study of samplesM2, M8, M19, M20, M22, M23, M1 and M14 (the samples with thegreatest number of experimental points) was conducted. Those soilswith 6 (M2, M8, M19, M20, M22 and M23) and 7 points (M1 andM14) were the ones used, so every possible combination of 3 pointswas studied (20 different combinations were obtained in each 6-pointsoil and 35 in each 7-point soil, i.e. there were 190 combinations intotal). Bending curveswere determined fromeach 3-point combination,so that the same extra points as those included in Table 3 were calculat-ed from thebending curve equation. The 3 experimental points togetherwith the extra points were used to draw the stiff-plastic lines and soft-plastic lines and thus, PL, BL and SSLwere obtained and compared to theoriginal 6 or 7 experimental point results (the reference). In accordancewith the maximum acceptable difference for two PL results as statedin UNE103104 -93, those results obtained from the use of just 3 exper-imental points that differed by more than 2 percentage points with re-spect to the reference were considered to be inaccurate. Since alarge amount of data was extracted, Table 5 shows a summary of the re-sults. The overall percentage of correct (accurate) results was very high(91.1% for PL, 83.7% for BL and 98.4% for SSL). Moreover, there was astrong relationship between the bending slope, m, and the number ofcorrect results. The average of the bending slope, m, in the soils tested(without the 3-point soils M11, M15 and M17) was 0.108 with a stan-dard deviation of 0.033 (m values are shown in bold in the bendingequations in Table 3). Then, there was an excellent success percentage(PL = 99.3 %, BL = 87.0% and SSL = 100%) with the data calculatedfrom a bending curve equation in which m had a value between 0.058and 0.158 (1.5 standard deviation range). These are also shown inbold in Table 5. In contrast, for m values outside the 1.5 sd range (i.e.m N 0.158 or m b 0.058) the percentage of inaccurate data rose, so thesuccess percentage dropped to only 63.6% for PL, 72.7% for BL and93.2% for SSL. Therefore, a very quick 3-point method was feasible soif the experimental bending slope is between 0.058 and 0.158 the re-sults can be considered correct and if m is outside this range, thenobtaining more experimental points is recommended. Hence, theM11, M15 and M17 results were correct since their bending slopes laybetween said range.

3.6. A one-point thread bending method

The liquid limit of soil was calculated using international standardsby means of an equation dependent on the most probable slope of theow line from a statistical point of view (e.g. this slope was 0.117 forUNE 103-103-94, and 0.121 for ASTM D 431805).

By using the same principle, with only one experimental point thestiff-plastic and soft-plastic lines could be calculated and with themthe PL, BL and SSL. The bending slope, m, of the 24 tested soils was0.108 with a standard deviation of 0.032 (Table 3), from which the fol-lowing equation was obtained:

Wextra Wexp Bexp=Bextra 0:108 10

whereWexp and Bexp show thewater content and the point bending ob-tained experimentally, respectively. Bextra is the bending of the extrapoint added in the analysis and Wextra is the water content of that

extra point.

Every point was substituted into Eq (10). The extra points (Bexp)were those indicated in Table 3. Each experimental point togetherwith its extra points were plotted and the stiff-plastic and soft-plasticlines were drawn. PL, BL and SSL were calculated and compared withthe results for all the points shown in Table 3. Those results that differedby more than 2 percentage points with respect to the reference wereconsidered to be inaccurate. As can be seen in Table 6 said resultswere highly satisfactory. From a total of 119 results, 108 for PL and107 for SSL were highly accurate since they differed by less than 2percentage points with respect to the reference, i.e. for these two pa-rameters 90.8% and 89.9% of results were accurate. There was a greaterdeviationwith BLwhichhad a success percentage of 68.9%. Thus, in gen-eral all soils showed excellent results with the one-point test. This wascorroborated in Fig. 12, where the average results of the one-point testwas plotted against the reference results with all the original points.Only the soils M8 and M9 showed deviation with the BL results(Fig. 12b), whereas for all other data there was excellent concurrencein the graphs, with high correlations (R2 of 0.976, 0.907 and 0.986 for

the thread bending test is not only more accurate but also quickerthan the thread rolling test in PL determination.

4. Conclusions

The thread rolling test is inadequate for determining the PL, as it ishighly dependent on the skill and judgment of the operator who is car-rying out the test. However its simplicity, low cost and speed give it anadvantage over the unsuccessful alternatives proposed to date.

For this reason, the method presented in this paper (the threadbending test), based on the measurement of bending deformations,has been presented as a real alternative with potential to replace theoutdated thread rolling test and to become normalized, because apartfrom being simple, rapid and inexpensive, it is also accurate and freeof subjective judgments.

Additionally, the newparameters dened by the thread bending testallow other soil consistency states apart from the typical plastic and liq-uid states to be identied, which will certainly be useful in sectors such

e w

5.320.43.56.623.77.720.247.20.024.77.431.942.62.47.8

Table 5Summary of the results of 190 combinations of 3 points from those soils tested with 6 and 7 points and relationships regarding the bending slope, m.

PL BL SSL

Total number of 3-point combinations 190 190 190Total number of correct results and (% success) 173 (91.1) 159 (83.7) 187 (98.4)No. combinations within the range 1.5 sd (0.058 bm b 0.158) 146 146 146No. of correct results and (% success) within the range 1.5 sd 145 (99.3) 127 (87.0) 146 (100)No. combinations outside the range 1.5 sd 44 44 44No. of correct results and (% success) outside the range 1.5sd 28 (63.6) 32 (72.7) 41 (93.2)

507J.M. Moreno-Maroto, J. Alonso-Azcrate / Applied Clay Science 114 (2015) 497508PL, BL and SSL respectively) and regression lines that tted very closelyto the 1:1 line, so this one-point test could be considered to be as reli-able a method as the multi-point test. In order to improve accuracyeven more, two experimental points with different B values are recom-mended in this one-point test and if the differences are not greater than2 percentage points, the test can be considered satisfactory with thenal result being the average of the two experimental points. If thesediffer by more than two percentage points, more experimental datashould be obtained. As a nal point, it can be said that this version of

Table 6Results of the one-point bending method for each point experimentally obtained. Data arreference.

Soil Reference Point 1 Point 2 Point 3

M1 19.1; 32.0; 25.1 18.8; 31.5; 25.6 19.6; 31.1; 25.4 20.1; 30.9; 2M2 15.9; 26.9; 20.8 16.6; 24.7; 20.4 16.2; 23.8; 29.7 16.7; 24.7;M3 19.7; 28.8; 24.2 19.1; 30.3; 24.7 19.1; 28.8; 23.6 19.0; 28.8; 2M4 12.4; 19.7; 16.1 12.8; 18.7; 16.0 12.9; 19.0; 16.0 13.2; 19.4; 1M5 21.8; 28.0; 25.0 21.1; 32.4; 26.5 21.6; 32.7; 26.8 19.9; 30.2;M6 13.6; 22.1; 18.0 14.0; 24.2; 19.6 13.9; 22.1; 17.9 13.7; 22.7; 1M7 14.9; 26.8; 20.8 14.9; 24.5; 19.9 16.2; 25.0; 20.4 17.8; 27.0;M8 32.8; 85.0; 54.8 32.7; 55.8; 43.7 34.8; 58.2; 45.6 36.2; 60.2;M9 52.9; 77.5; 63.6 52.4; 90.8; 71.1 54.0; 86.0; 66.9 55.2; 89.0; 7M10 20.9; 27.4; 24.3 21.0; 35.2; 28.6 20.6; 32.3; 26.3 20.1; 30.7;M11 12.9; 20.9; 17.2 12.9; 19.1; 16.3 13.6; 19.9; 17.0 13.9; 20.3; 1M12 24.3; 41.6; 32.5 24.5; 38.8; 31.6 25.6; 38.7; 31.7 25.7; 38.9;M13 36.2; 47.7; 41.9 34.9; 53.6; 43.8 35.1; 51.9; 42.8 35.2; 52.3;M14 17.5; 27.5; 22.7 17.9; 26.4; 22.5 17.3; 25.3; 21.6 17.9; 26.3; 2M15 15.0; 21.4; 18.3 14.6; 21.6; 17.8 14.9; 22.1; 18.2 14.5; 21.5; 1

M16 15.4; 22.3; 19.2 15.4; 22.3; 19.2 15.3; 22.5; 19.2 15.5; 22.7; 19.4M17 16.8; 23.4; 20.4 16.4; 24.1; 20.6 15.8; 23.4; 19.5 16.1; 23.6; 20.1M18 15.6; 22.8; 18.8 16.3; 25.4; 21.5 16.6; 24.4; 20.8 15.8; 23.0; 19.7M19 11.6; 20.0; 14.8 12.8; 18.9; 15.6 12.2; 18.1; 15.0 12.0; 17.8; 14.7M20 19.2; 26.0; 23.6 19.1; 29.8; 24.5 18.1; 26.8; 22.1 18.0; 26.6; 21.8M21 11.5; 19.1; 15.2 12.5; 18.4; 15.4 12.4; 18.2; 15.3 12.1; 17.8; 15.2M22 15.9; 22.9; 19.1 15.8; 25.3; 20.6 15.4; 23.2; 19.0 16.0; 24.2; 19.8M23 17.4; 25.8; 20.8 17.3; 27.3; 22.3 17.2; 26.1; 21.3 17.1; 25.8; 21.3M24 14.3; 23.5; 18.9 14.4; 22.5; 18.4 15.1; 22.9; 18.8 15.1; 22.9; 18.8

NOTE: The points are in ascending order of bending, i.e., the Point 1 is the onewhose experimenpoints) is the one with the highest B.NA: Not applicable.as the ceramics industry, agriculture and geotechnical engineering.

Acknowledgments

This research has been partially funded by a grant (Beca deInvestigacin Ambiental) from the Servicio de Medio Ambiente de laDiputacin Provincial de Toledo (grant number 133/10) in 2010 andthe research project PEII-2014-025-P of the Junta de Comunidades deCastilla-La Mancha.

ritten as PL; BL; SSL. In bold those results that differ in more than 2 points respect to the

Point 4 Point 5 Point 6 Point 7

19.3; 29.3; 23.9 19.7; 29.8; 24.4 20.9; 31.6; 26.0 21.6; 32.8; 26.817.7; 26.2; 21.6 17.2; 25.4; 21.0 17.8; 26.4; 21.8 NA19.9; 30.2; 24.8 NA NA NA13.0; 19.0; 16.2 13.1; 19.2; 16.4 NA NA19.5; 28.9; 23.8 NA NA NA14.8; 23.7; 19.2 13.8; 22.0; 17.9 NA NA16.9; 25.7; 21.0 17.2; 26.1; 21.3 NA NA40.7; 64.9; 51.1 45.5; 71.3; 57.3 44.9; 70.2; 56.5 NA54.1; 83.7; 66.3 53.9; 84.1; 65.7 NA NA20.2; 30.6; 24.8 19.5; 29.6; 24.2 NA NANA NA NA NA26.3; 39.9; 32.6 27.3; 41.4; 34.0 NA NA32.8; 48.6; 40.1 NA NA NA17.5; 25.7; 21.9 18.0; 26.3; 22.5 18.6; 27.3; 23.3 18.6; 27.3; 23.2NA NA NA NA

15.7; 23.1; 19.3 15.1; 22.1; 18.8 NA NANA NA NA NA15.5; 22.7; 19.4 15.6; 22.8; 19.5 NA NA12.5; 18.5; 15.3 13.2; 19.6; 16.2 13.6; 20.0; 16.6 NA19.4; 28.7; 23.7 18.0; 26.6; 22.0 18.6; 27.5; 22.8 NA12.3; 18.0; 15.4 13.0; 19.0; 16.2 NA NA15.7; 24.0; 19.4 14.7; 22.3; 18.3 15.7; 23.6; 19.5 NA16.4; 24.9; 20.4 16.5; 25.1; 20.6 17.6; 26.6; 21.9 NA15.4; 23.4; 19.2 NA NA NA

tal B is the lowest whereas the point 7 (or the applicable in those samples with less than 7

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